1. Field of the Invention
The invention relates to a control unit for a medical apparatus of the type having a front panel in which at least one setting knob and/or a switching knob is located.
2. Description of the Prior Art
A control unit is known through a service manual 10 for Servo Ventilator 900B, Siemens-Elema AB, Publication No. S1080 Oct. 5, 1980 and having a front panel with setting knob assemblies that control potentiometers for setting of a number of different ventilator functions. A knob assembly includes a turning knob on the front of the front panel, which turning knob is screwed onto a feed-through shaft, which passes through a hole in the front panel to the potentiometer. The feed-through shaft is fastened axially in the front panel with a nut on the back side of the front panel and a locking nut on the front. To protect the control unit from the penetration of liquid, the front panel is covered with a thin protection plate of plastic. At the hole through the front panel, the locking nut prevents liquid from penetrating by its pressure against the front panel.
The setting knobs of the control unit cannot, however, be fixed so as to remain precisely at the set positions, which means that a setting can be changed by mistake. There is also a risk that the potentiometer or the turning knobs may break, as the force applied to the turning knob is directly transferred to the potentiometer via the feed-through shaft.